1. Field of the Invention
The present invention relates to a radio broadcast/multicast service provided in a universal mobile telecommunications system (UMTS), and more particularly, to a method and apparatus for establishing a radio bearer of a point-to-multipoint multimedia service by utilizing a reference configuration of radio bearer parameters, for example protocol parameters and channel parameters, for quickly establishing a radio bearer when a user equipment (UE) moves between cells.
2. Discussion of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system that is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A conventional UMTS network structure 1 is illustrated in FIG. 1. One mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and core network 4 to meet end-to-end quality-of-service requirements.
The UTRAN 6 includes a plurality of radio network subsystems 8, each of which comprises one radio network controller (RNC) 10 and a plurality of base stations 12, or “Node Bs.” The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit downlink signals to the UE. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer of the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and UTRAN 6 is realized through a radio interface protocol established in accordance with 3GPP radio access network specifications describing a physical layer (L1), a data link layer (L2), and a network layer (L3). A control plane is provided for carrying control information for the maintenance and management of the interface and a user plane is provided for carrying data traffic such as voice signals and Internet protocol packet transmissions. The conventional architecture of the radio interface protocol is illustrated in FIG. 2.
The physical (PHY) layer provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. The MAC layer includes a MAC-b entity, a MAC-d entity, and a MAC-c/sh entity.
The MAC-b entity manages the broadcast channel as a transport channel responsible for the broadcasting of system information. The MAC-c/sh entity manages common transport channels shared with other UEs 2 within the cell, for example the forward access channel and downlink shared channel, such that one MAC-c/sh entity exists for each cell and is located at the controlling RNC 10. Therefore, each UE 2 has one MAC-c/sh entity. The MAC-d entity manages a dedicated transport channel with respect to a specific UE 2 such that the MAC-d entity is located at the serving RNC 10 and each UE also has one MAC-d entity.
To provide a point-to-point service, such as a multimedia broadcast/multicast service (MBMS), in accordance with a conventional method of the present invention, an MBMS function is appended to the functions of the MAC-c/sh layer, thereby creating a MAC-c/sh/m layer. There is one MAC-c/sh/m layer per cell in the UTRAN 6 and one MAC-c/sh/m layer per UE.
A radio link control (RLC) layer supports the transmission of reliable data and is responsible for the segmentation and concatenation of RLC service data units delivered from a higher layer. The size of the RLC service data unit is adjusted for the processing capacity in the RLC layer and a header is appended to form an RLC protocol data unit for delivery to the MAC layer.
The formed units of service data and protocol data delivered from the higher layer are stored in an RLC buffer of the RLC layer. The RLC services are used by service-specific protocol layers on the user plane, namely a broadcast/multicast control (BMC) protocol and a packet data convergence protocol (PDCP), and are used by a radio resource control (RRC) layer for signaling transport on the control plane.
The BMC layer schedules a cell broadcast message delivered from the core network 4 and enables the cell broadcast message to be broadcast to the corresponding UEs 2 in the appropriate cell. Header information, such as a message identification, a serial number, and a coding scheme, is added to the cell broadcast message to generate a broadcast/multicast control message for delivery to the RLC layer.
The RLC layer appends RLC header information to the broadcast/multicast control message and transmits the message to the MAC layer via a common traffic channel as a logical channel. The MAC layer maps the common traffic channel to a forward access channel as a transport channel. The transport channel is mapped to a secondary common control physical channel as a physical channel.
The PDCP layer transfers data efficiently over a radio interface having a relatively small bandwidth. The PDCP layer uses a network protocol such as IPv4 or IPv6 and a header compression technique for eliminating unnecessary control information utilized in a wire network. The PDCP layer enhances transmission efficiency since only the information essential to the header is included in the transfer.
The RRC layer handles the control plane signaling of the network layer (L3) between the UEs 2 and the UTRAN 6 and controls the transport and physical channels for the establishment, reconfiguration, and release of radio bearers. A radio bearer is a service provided by a lower layer, such as the RLC layer or MAC layer, for data transfer between the UE 2 and UTRAN 6 in order to guarantee a predetermined quality of service by the UE 2 and UTRAN 6.
Establishment of a radio bearer determines the regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission of messages between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
An MBMS provides a streaming or background service to a plurality of UEs 2 using a downlink only MBMS radio bearer. In the UTRAN 6, an MBMS may utilize a point-to-multipoint or point-to-point radio bearer.
In the MBMS broadcast mode, multimedia data is transmitted to all UEs 2 within a broadcast area, for example the domain where the broadcast service is available. In the MBMS multicast mode, multimedia data for a specific UE group is transmitted within a multicast area, for example the domain where the multicast service is available.
An MBMS requires the support of two logical channels; an MBMS control channel (MCCH), which is a point-to-multi point downlink channel for transmitting MBMS control information to UEs 2, and an MBMS traffic channel (MTCH), which is a point-to-multi point downlink channel for transmitting MBMS data to UEs. One MCCH channel exists in each cell, and one MTCH channel exists for each specific MBMS within a specific cell. Both logical channels are mapped to a transport channel (FACH) and a secondary common control physical channel (S-CCPCH).
FIG. 3 illustrates a conventional MTCH protocol in which an RNC 10 configuration has two Node Bs 12, with one managing three cells and another managing one cell. Each cell has separately configured radio bearer parameters for every PHY, RLC, and PDCP entity per MTCH channel per MBMS in the UTRAN 6 side. The same entities are similarly established in the UE side 2 (not shown).
In the conventional method, however, the UTRAN 6 independently configures and reconfigures radio bearer parameters for each cell. Therefore, despite providing the same service, the radio bearer parameter values may be configured differently, whereby protocol entities and channels may operate differently. Since a UE 2 needs to configure new protocol parameters whenever moving to another cell, there may be an undesirable delay before a radio bearer is newly established, during which time the UE has no radio bearer and thus receives no MBMS data. Data loss may occur when a UE 2 moves to a new cell and the UE is unable to achieve soft combining gain in which values from various cells are combined during a soft handover.
Therefore, there is a need for a method and apparatus for enabling a mobile terminal that moves between cells to reconfigure protocol parameters without data loss and to achieve soft combining gain via a soft handover. The present invention addresses these and other needs.